facial nerve parotid landmark

8/12/2019 Facial Nerve Parotid Landmark

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O R I G I N A L A R T I C L E

Identification of Facial Nerve During Parotidectomy: A CombinedAnatomical & Surgical Study

Somnath Saha Sudipta Pal Moushumi Sengupta

Kanishka Chowdhury Vedula Padmini Saha

Lopamudra Mondal

Received: 21 September 2012 / Accepted: 21 June 2013/ Published online: 24 July 2013

Association of Otolaryngologists of India 2013

Abstract To find out the most easily identifiable and

anatomically consistent landmark for identification offacial nerve during parotid surgery. Ten cadaveric dissec-

tions and ten live parotid surgeries for different types of

parotid tumours were done. Cadaveric dissection was per-

formed in the Department of Anatomy and the surgeries

were done in the Department of ENT and Head and Neck

surgery of R. G. Kar Medical College of Kolkata. The

distance of the facial nerve trunk from three most com-

monly used landmarks (viz., tympanomastoid suture, tragal

pointer and posterior belly of digastric muscle) was mea-

sured in both cadaver and live patients. The ease of iden-

tification of the nerve trunk using each of the landmarks,

particularly during live surgery was also assessed. The

mean distance of the tympanomastoid suture from the

facial nerve trunk was 3.5 mm (cadaver) and 3.87 mm(live surgery), the tragal pointer was found to be at a mean

distance of 16.61 mm (cadaver) and 16.36 mm (live sur-

gery) and in case of the posterior belly of digastric muscle

it was 7.41 mm (cadaver) and 8.03 mm (live surgery).

During live surgery the posterior belly of digastric was

found to be the most easily identifiable landmark with a

consistent anatomical relationship with the nerve trunk.

The posterior belly of digastric muscle is the most easily

identifiable and a very consistent landmark for facial nerve

dissection during parotidectomy. When supplemented with

the tragal pointer, accuracy in identifying the facial nerve

trunk is very high, thereby avoiding inadvertent injury to

the nerve trunk.

Keywords Facial nerve Parotidectomy

Posterior belly of digastric Tragal pointer

Introduction

Parotidectomy is basically an anatomical dissection. Iden-

tification of the facial nerve trunk is essential during sur-

gery of the parotid gland because facial nerve injury is the

most daunting potential complication of parotid gland

surgery owing to the close relation between the gland and

the extratemporal course of facial nerve. There are two

approaches to identify the facial nerve trunk during

parotidectomyconventional antegrade dissection of the

facial nerve, and retrograde dissection. Numerous soft tis-

sue and bony landmarks have been proposed to assist the

surgeon in the early identification of this nerve. Most

commonly used anatomical landmarks to identify facial

nerve trunk are stylomastoid foramen, tympanomastoid

S. Saha S. Pal M. Sengupta K. Chowdhury

Department of ENT, Head and Neck Surgery, R. G. Kar Medical

College & Hospital, Kolkata, India

e-mail: [email protected]

M. Sengupta


K. Chowdhury


S. Saha (&)

Sundaram Apartments, 91, Sarat Chatterjee Road, Barat, LakeTown, Kolkata 700089, India


V. P. Saha

Department of Plastic Surgery, R. G. Kar Medical College,

Kolkata, India


L. Mondal

Department of Anatomy, Calcutta National Medical College,

Kolkata, India


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Indian J Otolaryngol Head Neck Surg

(JanMar 2014) 66(1):6368; DOI 10.1007/s12070-013-0669-z


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suture (TMS), posterior belly of digastric (PBD), tragal

pointer (TP), mastoid process and peripheral branches of

the facial nerve. Use of so many landmarks to identify the

facial nerve trunk points to the fact that there is lack of

consensus regarding the safety and reliability of each of

these landmarks.

Aims and Objectives

The aim of the cadaveric dissection was to dissect all the

landmarks of facial nerve that has been described in the

literature and study their respective anatomical relationship

with the facial nerve. The three most easily identifiable and

anatomically constant landmarks were selected for dem-

onstration in live surgery and the findings were corrobo-

rated with that of the anatomical dissections.

Materials and Methods

Ten fresh cadaver dissections and ten live parotid surgeries

for different types of parotid tumours were done in the

present study. Standard incision (Modified Blairs) for

parotidectomy was used in both cadaver and live surgery. We

tried to identify and demonstrate all the landmarks for the

facial nerve and study their respective relations to the facial

nerve trunk in cadaver. The distance of the individual land-

mark from the facial nerve trunk was measured with the helpof slide callipers. In case of the bony landmarks the mea-

surement was taken from the bone itself; in case of the

posterior belly of digastric muscle the distance was measured

from the insertion of the muscle into the mastoid process. In

live surgery for different pathological conditions of parotid

gland, the three most easily identifiable and anatomically

constant landmarks were selected and their respective dis-

tance from the facial nerve trunk was measured. Live surgical

data was compared with that of the anatomical dissection.

Results

In the cadaver dissection the mean distance of the facial

nerve from the tympanomastoid suture line was 3.5 mm

(range 2.54.5 mm), in case of tragal pointer the mean was

16.61 mm (1421 mm) and posterior belly of digastric was

found to be at a mean distance of 7.5 mm from the trunk of

the facial nerve (range 69.5 mm) (Table1]; Figs.1,2). In

the live surgical patient group, the mean distance of the

tympanomastoid suture from the facial nerve was 3.87 mm

(26 mm)a little more than that in the cadaveric study.

The tragal pointer was at an average distance of 16.36 mm

the range being from 13.6 to 19 mm. The mean separation

of the posterior belly of digastrics muscle from the nerve

trunk during surgery was 8.03 mm (range 611.5 mm)

(Table2; Figs. 3, 4).

Discussion

Facial nerve injury is the most common complication of

parotid surgery as the two structures are intimately related

to each other. This is because of the fact that during

embryogenesis, the parotid gland entraps mesenchymal

structures which later develops into the facial nerve. The

facial nerve however is said to divide the gland into a deep

and superficial lobe but this concept is not anatomically

based. The facial nerve along with the accompanyingvessels creates a potential plane which lies in between the

deep and superficial lobes of the parotid gland. Dissection

in this plane is never possible until and unless the surgeon

identifies the nerve and proceeds along the nerve and its

branches. This clearly indicates to the fact that parotid

gland surgery is purely an anatomical dissection and sound

anatomical knowledge sharpened further by cadaveric

dissection goes a long way in improving the surgical skill

of a surgeon.

Table 1 Cadaver study:

distance of facial nerve trunk

from different anatomic

landmarks

Cadaver no Tympanomastoid

suture (in mm)

Tragal pointer

(in mm)

Posterior belly of

digastric (in mm)

1 2.5 14 6.3

2 3 18 7

3 3 15.5 8

4 2.5 18 6

5 3.7 16 7.56 2.8 14.6 6.8

7 3 16 8

8 4.5 21 7

9 3 17 9.5

10 3.5 16 8

64 Indian J Otolaryngol Head Neck Surg (JanMar 2014) 66(1):6368

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Postoperative facial nerve weakness can be temporary or

permanent. Temporary weakness is much more common

and incidence is between 10 and 50 % of parotidectomies

[1, 2]. The cause of temporary weakness is neurapraxia,

which results from a combination of trauma while dis-

secting right on the nerve, traction injury to the nerve, heat

injury secondary to use of electro-cautery, and prolonged

operating time. The incidence of permanent facial nerve

injury is generally reported as 0.5 % [1, 2]. The cause of

such weakness is due to transection of, or cautery injury to

the main trunk. In a large series from France comprising

131 patients of parotid tumour, Gaillard et al. reported that

there is a high percentage of facial nerve dysfunction

(42.7 % on the first postoperative day) immediately after

parotidectomy which gradually improves over time to the

tune of 30.7 % at 1 month post op and 0 % at 6 months

after the surgery. The marginal mandibular branch was

reported as the single most affected nerve branch following

parotidectomy (48.2 %). Facial nerve dysfunction after

total parotidectomy was found to be significantly higher

(P\ 0.001) than that in superficial parotidectomy (18.2 %

at day 1 and 10.9 % at month 1) [3].

In another study from Australia the authors reported that

the incidence of initial postoperative facial weakness var-

ied with the type of pathology and the extent of surgery. In

cases of limited superficial parotidectomy for superficial

lobe neoplasia the rates of initial facial nerve dysfunction

were 16.5 % for benign lesions and 13 % for malignant

tumours. But when near total parotidectomy was done for

deep lobe tumours the percentage increased to 31 % for

benign and 100 % for malignant lesions in the early post

operative period. Surgery for inflammatory lesions like

chronic sialadenitis was associated with relatively higher

facial palsy rates of 30 % for complete superficial

Fig. 1 Cadaveric dissection

showing relationship of the

facial nerve with the posterior

belly of digastrics muscle

Fig. 2 Cadaver dissection

specimen showing the facial

nerve, tragal pointerand theposterior belly of digastric

Indian J Otolaryngol Head Neck Surg (JanMar 2014) 66(1):6368 65

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parotidectomy and 34 % for near-total parotidectomy,

respectively. In cases of parotidectomy associated with a

neck dissection 83 % of patients had facial paresis and

33 % of cases had initial facial nerve dysfunction while

undergoing revision parotid surgery. In their series, per-

manent paralysis occurred in 13 (5.6 %) of 230 patients,

but 10 of these 13 had simultaneous neck dissection and

facial nerve dysfunction involved only the marginal man-dibular branch. In 46 of 67 of those with initial weakness

(68 %), normal facial movements recovered within

6 months [4].

In another series involving paediatric patients, the inci-

dence of immediate facial nerve paresis was 21 % (9/43).

In this series also the most common branch involved was

the marginal mandibular nerve (n = 7). Facial nerve

function recovered fully in all the cases within 6 months

[5].

In absence of facial nerve monitor, facial nerve is gen-

erally located by means of anterograde or retrograde dis-

section methods. Retrograde dissection is the lesscommonly used technique with the surgeons preferring this

method mostly during revision parotidectomy. Anterograde

dissection or proximal surgical identification technique is

aimed at identifying the facial nerve at its point of exit

from the stylomastoid foramen and is the preferred method

of dissecting the facial nerve.

Over the years, various authors have performed cadav-

eric dissection as well as live surgery to compare the dif-

ferent landmarks. Different available studies showing the

measurement of various landmarks from the facial nerve

trunk have been presented in Table3.

Though stylomastoid foramen is anatomically a very

constant landmark for facial nerve, but in live surgical

situation it is very difficult to find this foramen as it is

mainly a palpatory landmark and most importantly because

it remains surrounded by thick fascia which is continuous

with the periosteum of skull base. Excessive dissection in

this area very often leads to permanent paralysis of the

nerve.

The tympanomastoid suture line is palpable as a hard

ridge deep to the cartilaginous portion of the external

auditory canal. The facial nerve emerges a few millimeters

deep to its outer edge. Tympanomastoid suture can be

identified in the cadavers without much difficulty but in

live surgery it is basically a palpatory landmark and direct

visualization of the suture is practically not possible. In the

present study we found that the TMS lies about

2.54.5 mm (cad) and 26 mm (live) respectively from the

facial nerve trunk (Table 1). Witt et al. [6] stated that TMS

is a significantly closer and less variable anatomic land-

mark compared with the PBD both in cadaver dissection

and in live patients. In their prospective study of 14

cadaver specimens and 22 live patients, the mean closest

Fig. 3 Superficial parotidectomy in progress with display of the

facial nerve

Fig. 4 A deep lobe parotid tumour lying below the dissected facial

nerve

Table 2 Surgical study: distance of facial nerve trunk from different

anatomic landmarks

Surgical

patient

no

Tympanomastoid

suture (in mm)

Tragal

pointer

(in mm)

Posterior belly

of digastric

(in mm)

1 3.5 17.5 7.5

2 4 19 8

3 2.7 13.6 7

4 2 17 8.8

5 4.9 15 6

6 5.3 18.5 7.5

7 4 16 6.5

8 2.5 15 9.5

9 3.8 18 8

10 6 14 11.5


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distances from the TMS and PBD to the facial nerve were

1.8 (range 04) mm and 12.4 (range 717) mm, respec-

tively (P\ .05) for cadavers. The mean closest distances

in live patients from the TMS and PBD to the facial nerve

were 2.0 (range 04) mm and 10.7 (range 514) mm,

respectively (P\ .05). Bushey et al. [7] also showed in his

cadaveric study as tympanomastoid suture is a close andpredictable anatomic landmark that can be used to identify

the facial nerve trunk. In his study on 30 cadavers, the

distance from TMS to the facial nerve trunk ranged from

3.3 to 9.2 mm with a mean of 4.9 mm. In the study on 26

cadavers by Rea et al. [8] the main trunk of the facial

nerve was found 2.5 .4 mm from the TMS. Pather and

Osman [9] in their study on 40 cadavers found that the

facial nerve trunk was about 4.918.6 mm away from

TMS.

Tragal pointer is a very popular landmark and facial

nerve usually lies around 1 cm deep and inferior to the

pointer. The only drawback of the pointer is that it is a

cartilaginous structure which is mobile, asymmetrical and

has a blunt and irregular tip. In the present study we found

that it lies at a distance of about 14-21 mm (cad) and 13.5-

19 mm (live) from the facial nerve trunk respectively. In

the study on 26 cadavers by Rea et al. [8] the main trunk of

the facial nerve was found 6.9 1.8 mm from the TP. In

the study on 40 cadavers by Pather and Osman [9] the

facial nerve trunk was found 24.349.2 mm from the TP.

Mastoid process is also described as one of the land-

marks but the process lies deep to the insertion of the

sternocleidomastoid muscle and hence it is mainly a pal-

patory landmark. Greyling et al. [10] demonstrated that the

mean distance between the mastoid process and facial

nerve for the left was 9.18 2.05 mm and for the right,

9.35 1.67 mm on cadaver dissection.

During parotidectomy lateral retraction of the sterno-

cleidomastoid muscle exposes the posterior belly of digastric

muscle. This muscle is very easy to identify by the position

(just deep to sternomastoid) and also by the direction of the

muscle fibres that run towards the mastoid tip. The facial

nerve trunk lies approximately 1 cm above and parallel to

the upper border of the digastric muscle near its insertion at

the mastoid tip. In the present study, we found that the facial

nerve trunk lies at a distance of 69.5 mm (cad) and

611.5 mm (live) respectively from PBD and it has the

minimum anatomical variation. Rea et al. [8] demonstrated

that the main trunk of the facial nerve was found to lie

5.5 2.1 mm from the PBD. Pather and Osman [9] dem-onstrated that the facial nerve trunk was found 9.724.3 mm

from the PBD. Their results demonstrated that the posterior

belly of digastric, tragal pointer and transverse process of the

axis are consistent landmarks to the facial nerve trunk and

they advocated use of transverse process of axis as a pal-

patory landmarks as it does not require complex dissection

and ensures safety of the nerve [9].

However in cases of large tumours of the parotid gland

especially in malignant ones, the posterior belly of digas-

tric may become adherent to the tumour itself or to the

surrounding structures. In those cases this landmark may be

difficult to dissect or may not be in proper anatomical

location which calls for the use of another landmark. In this

situation the tragal pointer significantly helps in locating

the facial nerve trunk. In extreme cases even the tragal

pointer may be displaced and there the tympanomastoid

suture needs to be dissected which being a bony landmark

is rarely involved by the disease.

Facial nerve trunk can also be identified by performing

retrograde dissection whereby peripheral branches are

traced back to reach the main trunk. This technique is

sometimes needed on account of difficulty in locating the

main trunk, due to the presence of a post-inflammatory

fibrosis or overlying neoplasm. So peripheral branches can

also be considered to be one of the landmarks for the facial

nerve trunk, but in the absence of facial nerve stimulator it

is difficult to identify the peripheral branches which are

thin with wide anatomical variations. Sharma et al. rec-

ommended the use of buccal branch of facial nerve to

locate the main trunk. The reason behind was due to the

regular course and adequate size of this branch of facial

nerve in its peripheral area co-located with stensons duct,

which enabled it to be easily identified during surgery [11].

Table 3 Comparison of present study with similar studies published in literature

Clinical studies Distance from

PBDM

Distance from tragal

pointer

Distance from

TMS

Annals of Anatomy (Vol. 192, Feb 2010) Rea et al. [8] 5.5 2.1 mm 6.9 1.8 mm 2.5 0.4 mm

Surgical and Radiologic Anatomy (Vol. 28, Nov 2005) Pather and

Osman [9]

9.724.3 mm 24.349.2 mm 4.918.6 mm

The Laryngoscope (Vol. 115, April 2005) Witt et al. [ 6] 12.4 mm (cad) 1.8 mm (cad)10.7 mm (live) 2.0 mm (live)

Present study 69.5 mm (cad) 1421 mm (cad) 2.54.5 mm (cad)

611.5 mm (live) 13.519 mm (live) 26 mm (live)

Indian J Otolaryngol Head Neck Surg (JanMar 2014) 66(1):6368 67

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Pia et al. [12] used orbicular branch, on account of diffi-

culty in locating the main trunk of the nerve in 5 cases of

retrograde exploration of the nerve. Keefe et al. [13] used

postauricular branch to identify the main facial nerve trunk

in his study. Kanatas et al. [14] demonstrated the use of

digastric branch to identify the main trunk. In the present

study, peripheral branches were identified in the cadaveric

study and followed back to the main trunk. However in thelive surgery retrograde dissection was not required in any

of the cases.

Conclusion

Parotidectomy is a technically demanding operation. This

surgery becomes significantly less complicated for the

surgeon once he/she identifies the facial nerve trunk. For

easy and prompt identification of the nerve trunk, the

surgeon needs to systematically look for the anatomical

landmarks. The present study showed that the posteriorbelly of digastric is the best landmark to start with and in

case of difficulties in dissection or identification it may be

supplemented with the tragal pointer and the tympano-

mastoid suture line subsequently in that order.

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management of 246 previously untreated pleomorphic adenomas

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3. Gaillard C, Perie S, Susini B, St Guily JL (2005) Facial nerve

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dectomy. Arch Otolaryngol Head Neck Surg 123(10):10911096

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493494


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facial nerve parotid landmark

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